1. Field of the Invention
The invention relates to proteins of the mammalian sperm and oocyte, and uses thereof, e.g., in enhancing fertility and in contraception.
2. Background Art
Oocyte activation in mammals encompasses the resumption of second meiosis and the activation of anti-polyspermy defense, which are accompanied by calcium oscillations periodically crossing oocyte cytoplasm (reviewed by Schultz, R. M., and Kopf, G. S., “Molecular basis of mammalian egg activation,”in Current Topics in Developmental Biology, Pedersen, R. A., and Schatten, G. P., (eds), Vol. 30, Academic Press Inc., San Diego, (1995) pp. 21-62). In bovine and other mammals, the fertilization-induced oocyte activation is also accompanied by the assembly of nuclear pore complexes (NPC) into the cytoplasmic annulate lamellae (AL), and by the insertion of NPCs into a de novo-formed nuclear envelope (NE) of the female and male pronuclei (Sutovsky et al., J. Cell Sci. 111:2841-2854 (1998)). Three hypotheses were offered to explain the sperm-induced oocyte activation in mammals: The conduit, or calcium bomb hypothesis (Jaffe, L. F., Ann. N.Y. Acad. Sci. 339:86-101 (1980)) implicates the direct, sperm-generated “injection” of Ca2+ ions into oocyte cytoplasm at fertilization. The receptor hypothesis (e.g. Jones, K. T., and Whittingham, D. G., Dev. Biol. 178:229-237 (1996); Swann, K., Development 110:1295-1302 (1990)) maintains that the specific receptors on the sperm and oocyte plasma membranes activate a signaling cascade leading to the release of Ca2+ from internal stores in oocyte ER. Finally, the oscillogen hypothesis favors a soluble oscillogenic factor, presumably a polypeptide, which is released from the sperm head into the oocyte cytoplasm at the time of gamete fusion (Kimura, Y., et al., Biol. Reprod. 58:1407-1415 (1998); Parrington, J., et al., Nature 379:364-368 (1996); Perry, A. C. F., et al., Biol. Reprod 60:747-755 (1999)). Although there is a substantial amount of data in favor of each of the above hypotheses, and each of them may be relevant to certain animal taxa, recent studies seem to support the validity of the oscillogen hypothesis in mammals. The actual mechanism by which the spermatozoon introduces the oscillogenic molecules into oocyte cytoplasm is not known.
Perinuclear theca (PT) is a cytoskeletal coat of the mammalian sperm nucleus that is inserted between the nuclear envelope and the sperm plasma membrane (Bellvé, A. R., et al., Biol. Reprod. 47:451-465 (1992); Courtens, J. L., et al., J. Ultrastruct. Res. 57:54-64 (1976); Lalli, M., and Clermont, Y., Am. J. Anat. 160:419-434 (1981); Oko, R., and Clermont, Y., Biol. Reprod. 39:673-687 (1988)). During spermiogenesis, the PT attaches the acrosomal vesicle to the sperm nucleus and may be involved in shaping it (Oko, R., and Maravei, D., Biol. Reprod. 50:1000-1014 (1994); Oko, R., and Maravei, D., Microsc. Res. Tech. 32:520-532 (1995); Oko, R., and Clermont, Y., “Spermiogenesis,” in Encyclopedia of Reproduction, Knobil, E. and Neil, J. D., (eds.), Vol. IV, Academic Press Inc., San Diego (1998) pp. 602-609). At fertilization, the PT is removed from the sperm nucleus with the aid of oocyte's cortical microvilli (Sutovsky et al., Dev. Biol. 188:75-84 (1997)). Otherwise, an intact PT would constitute an unsurpassable hurdle preventing the access of the zygotic cytoplasm to the sperm nucleus, which at that time undergoes the remodeling into a male pronucleus. Recent studies of infertile men suffering from globozoospermy (Battaglia, D. E., et al., Fertil. Steril. 68:118-122 (1997); Edirisinghe, W. R., et al., Hum. Reprod. 13:3094-3098 (1998); Rybouchkin, A., et al., Hum. Reprod. 11:2170-2175 (1996)), a rare spermatogenic disorder in which the absence of PT causes the round shape of the sperm nucleus (Escalier, D., Int. J. Dev. Biol. 34:287-297 (1990)), demonstrated that such spermatozoa fail to induce oocyte activation after intracytoplasmic sperm injection (ICSI). Human and non-human primate oocytes are activated by ICSI with normal spermatozoa (Hewitson, L. C., et al., Biol. Reprod. 55:271-280 (1996); Palermo, G., et al., Lancet 340:17-18 (1992); Sutovsky, P., et al., Human Reprod. 14:2301-2312 (1996); Van Steirteghern, A., et al., Hum. Reprod. 8:1061-1066 (1993)) and the intracytoplasmic injection of crude (Swann, K., Development 110:1295-1302 (1990)) or partially purified (Kimura, Y., et al., Biol. Reprod 58:1407-1415 (1998); Perry, A. C. F., et al., Biol. Reprod. 60:747-755 (1999)) sperm extracts or demembranated sperm heads (Kimura, Y., et al., Biol. Reprod. 58:1407-1415 (1998)) activates rodent oocytes.